(a) Field of the Invention
The present invention relates to a plasma display panel. More specifically, the present invention relates to a display device and driving method for the purpose of maximizing a representation performance of low gray scales.
(b) Description of the Related Art
Various flat displays such as a liquid crystal display (LCD), a field emission display (FED), and a plasma display panel (PDP) have been developed. The plasma display panel has higher resolution, a higher rate of emission efficiency, and an wider view angle in comparison with other flat panel displays. Accordingly, the plasma display panel has come into the spotlight as a display that can be substituted for the conventional cathode ray tube (CRT), especially in the large-sized displays of greater than forty inches.
The PDP is a flat panel display for showing characters or images using plasma generated by gas discharge. The PDP can include hundreds of thousands to millions of pixels in a matrix format. With reference to FIG. 1 and FIG. 2, a configuration of the plasma display panel will be described.
FIG. 1 shows a partial perspective view of a PDP. As shown, the PDP includes two glass substrates 1, 6 facing each other, and scan electrodes 4 and sustain electrodes 5 are formed in pairs parallel on (or under) a first glass substrate 1 and covered with a dielectric layer 2 and a protection film 3. Address electrodes 8 are established on a second glass substrate 6, and address electrodes 8 are covered with insulator layer 7. Barrier ribs 9 are formed in parallel with address electrodes 8 on insulator layer 7 and between address electrodes 8. Phosphors 10 are formed on the surface of the insulator layer 7 and on both sides of the barrier ribs 9. First and second glass substrates 1, 6 are provided to face each other with a discharge space 11 between the glass substrates 1, 6 so that scan electrodes 4 and sustain electrodes 5 may respectively cross (or cross over) address electrodes 8. Discharge space 11 between an address electrode of address electrodes 8 and a crossing part of a pair of scan electrodes 4 and sustain electrodes 5 forms discharge cell 12, which is schematically indicated.
FIG. 2 shows an electrode arrangement of a PDP. As shown, the electrodes of the PDP have an n×m matrix format. Address electrodes A1 to Am are arranged in a column direction, and n scan electrodes Y1 to Yn and n sustain electrodes X1 to Xn are alternately arranged in a row direction. In the context of the following discussion, the scan electrodes can also be referred to as “Y electrodes” and the sustain electrodes can also be referred to as “X electrodes.” In addition, discharge cell 12 of FIG. 2 substantially corresponds to discharge cell 12 of FIG. 1.
A PDP divides a frame into a plurality of the subfields in order to be driven, and represents gray scales by the combination of respective subfields. Conventionally, each subfield comprises a reset period, an address period, and a sustain period. In the reset period, wall charges of a previous sustain-discharge are erased, and new wall charges are generated so as to stably perform the next address discharge. In the address period, cells that are turned on and the same that are turned off on the panel are selected, and the wall charges are accumulated to the cells that are turned on (i.e., addressed cells). In the sustain period, a discharge for substantially displaying images on the addressed cells is performed.
FIG. 3 shows a conventional PDP driving waveform diagram of certain subfields and emitted light from the subfields. The performance of the low gray scale representation performance is increased when a minimum discharge is generated in the subfield which represents minimum gray scales (units of light) in the PDP. As shown, light of the subfield with a weight of 1 for representing the minimum gray scales in the plasma display panel is given as a sum of light generated in the reset period, light generated in the selected cell in the address period, and light generated when one sustain-discharge is generated during the sustain discharging of the sustain period.
In particular, the reset period in the subfield with the weight of 1 includes a ramp rising period and a ramp falling period. A reset-discharge in the reset period is weak, and therefore light generated by the reset-discharge can be ignored. As such, the subfield with the weight of 1 for representing a gray scale 1 can be represented by only light generated in the address period (address light) and light generated in the sustain period (sustain light).
To improve efficiency of a PDP, a concentration of Xe of the discharge gas is increased, and therefore emission efficiency and brightness is increased. However, representation performance of low gray scales becomes a problem because a size of the unit of light generated by the sustain-discharging is increased when concentrations of high pressure gas and the Xe are increased in the PDP when the PDP is driven. Accordingly, there has been a limit in representing low gray scales in driving waveforms of a conventional PDP.
In particular for example, a considerable amount of light is emitted by the time of the sustain-discharge (sustain light) due to the address-discharge (address light) generated in the subfield with a weight of 1. As such, there is a need to reduce the address light itself for the purpose of effectively realizing low gray scales on a PDP because the emission of the address-discharge itself generates considerable brightness even if the emission of the one sustain-discharge pulse in the time of the sustain-discharge or sustain period is reduced.